The invention herein described relates generally to micro actuators and to head suspension assemblies of disk storage systems which utilize piezoelectric micro actuators as secondary actuators. Although the invention is principally described in relation to a magnetic disk storage device, those skilled in the art will appreciate that the principles of the invention may be used in other devices where micro actuators may be useful to effect controlled minute movements.
Magnetic disk storage devices (disk drives) include magnetic head suspension assemblies for the purpose of positioning and supporting a read/write transducer head relative to the surface of a rotating magnetic storage disk. A common construction of a head suspension assembly includes a load beam which has a mounting base portion at its proximal end, a relatively rigid portion at its distal end, and a spring portion between the mounting base portion and the rigid portion. The mounting base portion is mounted to a primary actuator which moves the head suspension assembly to position the read/write head over desired information tracks on the disk. A flexure is provided at the distal end of the load beam, which includes a slider mounted thereon for supporting the read/write head. The slider has an aerodynamic design so that it xe2x80x9cfliesxe2x80x9d via a lift force on an air bearing generated by the spinning disk. The flexure permits pitch and roll movements of the slider so that the head can follow disk surface fluctuations. The spring portion provides a spring force which counteracts the lift force of the slider in a known manner.
Disk drive manufacturers continue to develop smaller yet higher storage capacity drives. Storage capacity increases are achieved in part by increasing the density of the information tracks on the disks (i.e., by using narrower and/or more closely spaced tracks). As track density increases, however, it becomes increasingly difficult for the primary actuator to quickly and accurately position the read/write head over the desired track. For this reason, some manufacturers have incorporated secondary actuators which are supported by the load beam of the head suspension assembly. These suspension-based micro actuators are used to effect minute movement of the distal end portion of the load beam, and therefore the read/write head, relative to the proximal end portion of the load beam and independently of operation of the primary actuator.
Piezoelectric elements heretofore have been used as the micro actuators. The piezoelectric driven micro actuator is a simple and economically viable option for high track density (i.e., the number of concentric tracks per inch, or xe2x80x9cTPIxe2x80x9d) servoing. Some suspension-based micro actuators have employed two piezoelectric elements, or beams, working in the breathing mode (also known as the piezoelectric transverse effect 31 mode). In the prior art load beam suspension 1 shown in FIG. 1, two piezoelectric beams 2 sit piggyback on top of the load beam 3 on either side of a centrally located hinge portion 4. The beams 2 work in a push-pull manner and the hinge portion 4 transforms a substantially linear 31 mode action into a rotation which is amplified by the leverage of the load beam (the length of the portion of the load beam that is rotated upon actuation of the piezoelectric beams), causing the tip 5 of the load beam to deflect a few microns in the cross-track direction.
Applicant has appreciated that of all the actuating modes of a piezoelectric element, the breathing mode has the advantage of providing a large displacement in the 31 sense, which is proportional to the longitudinal vibration in the lengthwise direction of the element. In order to conserve mass and maximize the stroke length, it is desirable to use a relatively long, narrow and thin piezoelectric beam. A formidable challenge to using such a piezoelectric structure in a suspension load beam is the structural interface between the piezoelectric beams and the load beam. The piezoelectric beams typically have a minimum thickness of 0.2 mm (typical value) for providing sufficient structural strength whereas the load beams typically have a relatively smaller thickness (typically 0.1 mm). Because of their extremely thin structure, it is difficult to form a reliable bond between the thickness sides, or edges, of the load beam and the piezoelectric beam, although such an interface is the ideal approach to optimizing the aforedescribed breathing mode.
Some manufacturers glue the flat side of the piezoelectric beams on top of the load beam surface as shown in FIG. 1. However, while working in the breathing mode, the piezoelectric beams also expand and contract in the thickness direction, or 33 sense of movement (also known as the piezoelectric longitudinal effect 33 mode). Because the load beam is glued to the piezoelectric beams, this 33 movement causes out-of-plane movements of the load beam. In the aforedescribed two beam design, this also causes the load beam to twist (roll). Such a phenomenon affects the altitude (i.e., fly height) and attitude (i.e., roll angle) stability of the slider. In turn, this undesirably affects the PES transfer function and OTC of the system.
An inherent problem with the push-pull actuator arrangement of FIG. 1 is that performance depends upon the characteristics of the individual actuator elements. A high degree of linearity and symmetry are desirable in their performance. The same considerations also apply to the passive components that go into the mechanical load circuits of the individual actuators. In the case of dual piezoelectric beam actuators, it is desirable to have identical piezoelectric beams, adhesive attachments and electric driving circuits working in their linear ranges. However, such identity is difficult to realize from a practical standpoint. For example, the physical dimensions, d33-constant and elasticity of the two piezoelectric beams vary depending on their manufacturing conditions. Environmental, temperature and aging characteristics of the piezoelectric beams could be entirely different. Similarly it is difficult to attain identical area and thickness of the glue layers of the two piezoelectric beams. These factors can cause unsymmetrical twist of the load beam during its operation. Test results on a few samples of a dual piezoelectric beam micro actuator have shown large variations in stroke symmetry, resonance frequencies and damping.
The present invention provides a micro actuator driven load beam mechanism for use in a head suspension assembly that overcomes one or more drawbacks of prior art load beam mechanisms. According to one aspect of the invention, a load beam mechanism comprises a load beam including a proximal end portion, a distal end portion and a hinge portion connecting the proximal and distal end portions of the load beam for permitting relative movement therebetween in a hinge plane; and a piezoelectric beam connected between the proximal and distal end portions, the piezoelectric beam being selectively energizable to effect relative movement between the proximal and distal end portions. In accordance with the invention, the load beam includes a pocket for retaining at least one end of the piezoelectric beam.
In an embodiment, the piezoelectric beam is retained by the pocket in a plane inclined relative to the hinge plane.
In an embodiment, the pocket is formed by longitudinally opposed catches having oppositely facing attachment surfaces to which opposite face surfaces of the piezoelectric beam are attached, respectively.
In an embodiment, the longitudinally opposed catches extend in opposite directions from the hinge plane.
In an embodiment, the opposed catches hold the piezoelectric beam at an incline relative to the hinge plane.
In an embodiment, the piezoelectric beam is shrunk fitted between the catches.
In an embodiment, the catches have slots for retaining respective ends of the piezoelectric beam.
In an embodiment, the catches are inline with the hinge plane.
In an embodiment, there is only one piezoelectric beam.
According to another aspect of the invention, a micro actuator driven load beam mechanism for use in a head suspension assembly, comprises a load beam including a proximal end portion, a distal end portion and a hinge portion connecting the proximal and distal end portions of the load beam for permitting relative movement therebetween in a hinge plane; and a piezoelectric beam connecting the proximal and distal end portions, the piezoelectric beam being selectively energizable to effect relative movement between the proximal and distal end portions. In accordance with the invention, the piezoelectric beam is disposed in a plane that is inclined relative to the hinge plane.
In an embodiment, the proximal and distal end portions have oppositely facing attachment surfaces to which opposite face surfaces of the piezoelectric beam are attached.
In an embodiment, the attachment surfaces are offset in opposite directions from the hinge plane.
In an embodiment, the face surfaces of the piezoelectric beam are bonded as by gluing to the attachment surfaces.
According to a further aspect of the invention, a micro actuator driven load beam mechanism for use in a head suspension assembly, comprises a load beam having a longitudinal center axis, and including a proximal end portion, a distal end portion and a hinge portion connecting the proximal and distal end portions for permitting relative movement therebetween, the hinge portion being disposed in offset relation to the center axis of the load beam; and a piezoelectric beam connecting the proximal and distal end portions and being transversely centered with respect to the center axis of the load beam, the piezoelectric beam being selectively energizable to effect relative movement between the proximal and distal end portions.
In an embodiment, the hinge portion includes a pair of edge portions and a relatively narrower portion therebetween, the edge portions being connected to the respective proximal and distal end portions.
In an embodiment, there is only a single piezoelectric beam.
The foregoing and other features of the invention are hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail illustrative embodiments of the invention. These embodiments, however, are but a few of the various ways in which the principles of the invention may be employed.